In medium bowl, add 3/4 cup of the frosting and food color to desired shade of green; mix well. Spoon tinted frosting into decorating bag fitted with 1/8 to 1/4 inch round tip. Insert tip in center of 1 cupcake, about halfway down. Gently squeeze bag, pulling upward until cupcake swells slightly and filling comes to top. Repeat with remaining cupcakes.